Polymerization of ethylene



Patented Aug. 12, 1947 POLYMERIZATION F ETHYLENE Merlin Dewey Peterson, Oak Ridge, Tenn., assign-.

or to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application February 18, 1944,

Serial No. 522,964

a Claims. (01. 260-94) This invention relates to chemical processes and more particularly to improvements in the catalytic polymerization of ethylene.

This application is a continuation-impart of U. S, Patent 2,391,920, filed November 16, 1942.

It is known that ethylenic compounds can be polymerized with the aid of catalysts of the active oxygen or peroxide type, for example, benzoyl peroxide or the salts of persulfuric acid. These or under superatmospheric pressureuntil the desired degree of polymerization has been attained. Generally, the polymerization is conducted in vessels which are either constructed of or lined with glass, stainless steel, silver, copper, aluminum, mild steel, etc.

The polymerization can be carried out in a medium which may consist wholly of water, which may contain water in substantial amount, or which may consist solely of an organic solvent.

commonly used catalysts have many shortcom- If desired, however, the reaction can be carried ings, e. 8., limited temperature range of operabilout in the absence ofsolvents or diluents. ity (0 C. to about 110 C.) and restricted utility As a rulethe amount of catalyst will vary from in the polymerization of ethylenic compounds reabout 0.001% to about 5%, on the total weight quiring higher polymerization temperatures, of materials charged into the reaction vessel. It This invention accordingly has as an object to is generally preferred to use as low an amount proiride anew and improved method for polymerof catalyst as. possible and the range which has izing ethylene. A further object is the utilization been found satisfactory is from 0.01% to 1%, on or a novel type of catalyst for its polymerization.- the total weight of materials charged into the re- A still further object is to provide a, p0lymerizaactor. v tion process which is free from the restrictions In polymerizations in aqueous systems, discharacterizing polymerization processes involving persing or surface active agents may be used to catalysts of the active oxygen type. Other obmaintain anemulsifled state.- The pH of the sys- Jects will appear hereinafter; tem is not a critical factor for operativeness. In The above and other objects described hereinsome instances, however, it is desirable to operate after are accomplished by conducting the polyunder selected pH conditions in order to obtain merization of ethylene in the presence of catalytic optimum results from the standpoint of yields amounts of a dialkyl dioxide. and polymer quality. By dialkyl dioxide is meant dialkyl deriva-" In batch operations more of the ethylene being tives of hydrogen peroxide corresponding to the polymerized can be introduced as the reaction formula ROOR'. wherein R and R are-the same proceeds to'maintain the pressure in the system or different simple unsubstituted alkyl groups -in the range desired. 1 such as methyl, ethyl, propyl, etc. Examplesof The diallrylv dioxides of this invention are susuch dialkyl dioxides are dimethyl dioxide, diperior to other commonly used catalysts for the ethyl dioxide, dipropyl dioxide, propyl ethyl dibulk, solution, and emulsion polymerizations of oxide, propyl methyl dioxide, and the like. ethylene and for catalyzing its interpolymeriza- The dialkyl dioxides are prepared by reacting tion with other polymerizable organic compounds hydrogen peroxide in the presence of alkali with having ethylenic unsaturation, the appropriate dialkyl sulfate at 30 to 100 C. The examples which follow are submitted to il- These compounds are not to be confused with the lustratc and not to limit this invention. Unless ether peroxides which result from the action of 40 otherwise stated-parts are by weight. j air and light on dialkyl ethers and which in some v Example 1.A stainless steel pressure reactor instances have been referred to erroneously as diis flushed with oxygemfree nitrogen and charged alkyl dioxides. The true dialkyl dioxides arediswith 100 partsordeaerated, distilled water and tinguished from the monoalkyl and acyl deriva- I 0.4 part of diethyl dioxide. After removal of the tives of hydrogen peroxide in being much more nitrogen by evacuation, the reactor is charged chemically inert than the latter compounds and with ethylene to a pressure of 300 atmospheres giving a. negative test for active oxygen. and heated to 150 C. .Upon reachingthis tem- The polymerization of ethylene with dialkyl di- Derature' the ethylene pressure is raised to beoxides can be carried out either as a batch, semitween 900 and'lOOO atmospheres, the vessel agicontinuous, or continuous operation, in which a tated and the polymerization allowed to proceed suitable reaction vessel is charged with the catunder these conditions ior 8 hours. The-total alyst and the ethylene alone or with compounds pressure drop during this time is'about 40o at+ with which it is to be poleymerized, and the mixmospheres. The reactor is cooled, the excess ture heated either under autogenous pressure ethylene bled oil, and the Vessel then opened.

There'is thus obtained 34 parts of a white, solid, v

aaaaesa polymer having a melting point of 110 to 115 C.. l

in., as measured on, a hot pressed film prepared at 135 C. and 8000 lbs/sq. in. pressure. The polymer is soluble to an extent oi! about 20% by weight in hot xylene and from such solutions transparent films can be cast. Strips of hot pressed film can be elongated about 600 to 100%, by cold'drawing. i,

Duplication of the above experiment using benzoyl peroxide in place oithe diethyl dioxide yields 4.9 parts ofa light tan, brittle, wax having ing from the aqueous phase. This polymer, after a molecular weight of about 91 5 (ebullioscopic method). I v

Example 2.A stainless steel lined pressure reaction vessel is swept with nitrogen and thencharged with .100 parts; of deaerated distilled water, 1 .part of borax, and 0.4 part of diethyl dioxide. occupies about of the total space in the reactor. The reactor is closed, ethylene is admitted to a pressure, of about 1000 atmospheres, 25

and'the vessel heated to 130 C. with agitation. At the end of 8.5 hours the vessel is allowed to cool, the excess ethylene bled oil, and the vessel 1 opened. During this time the pressure is main tained at the indicated value by periodically'reo pressiuing with ethylene. There results 49 parts of a white solid ethylene polymer having an exg ethylene pressure is maintained in the indicated trusion rate 01.0.20 gram per minute at 190 C.

under 25 lbs. nitrogen pressure from an -orifice in diameter and V in length.' The tensile 5 strength of the polymeris 2020 lbs/sq. in. Thepolymer is soluble'to the extent of aboutv 20% in refluxing xylene and a hot pressed film thereofhas an elongation ofv about 450%.

Example 3.A solution of parts of vinyl acetate in parts or isooctane is placedin -a stainless steel reaction vessel together with 0.5 part of diethyl dioxide. After'closure, the airisremovedby evacuation and ethylene is forced in to a pressure of about 600 atmospheres and the 45 vessel gradually heated to 150 C. withagitation.

The ethylene pressure is adjusted to between 900 and 1000 atmospheres and maintained in this ture there is recovered 52 parts otfa hard wax like ethylene/vinyl acetate polymer having an'i n*- trinsic viscosity of 0.24 (measured as a 0.125%

solution in xylene at -C.).

isms-m1.

merizationwith ethylene in the manner described '0 vinylphthalimide containing 4.4% nitrogen irom 1 wh h it may be calculated that the ethylene/1W- dioxide as the catalyst. This charge ismai'ntained in Example-2,100 parts of isooctanerbeing used: as the reaction medium and-0.25 part oridiethyl,

with agitation at 150 to 200 C. under an ethylene pressure of 900 to 1000 atmospheres for 8 hours. 165.

From the reaction mixture there is obtained 101 tion vessel is swept free from atmosphericoxygen ethyl dioxide and 2 parts or borax.

' atmospheres. the reactor is cooled and the unreacted gases bled oil. Upon opening the reactor there is found This charge, which has -a pH of 9.2

The vessel is then cooled and the contents discharged. From the-reaction mix- 50 of distilled deoxygenated water, 0.5 part of div The vessel is closed and charged with ethylene to a pressure oi. 450 atmospheres, and then carbon monoxide is'added until the total pressure is 500 atmospheres.

The charged reactor is heated with agitation at 132 to 153 C. for 8.5 hours, during which time the pressure is maintained at 840 to 915 atmospheres by periodically repressuring with ethylene. The total observed pressure drop is 215 At the end of the reaction period 2 2.1 parts of a white, wax-like polymer of ethylene and carbon monoxide. This is isolated by filterwashing and drying, melts at 88 to 90 C. and

Its intrinsic viscosity is 0.15 (measured as a 0.125% solution in meta-cresolat 25 C.).

' Example 6.-A silver lined reaction vessel is charged with 50 parts of distilled, deoxygenated water, 50 parts of trioxane (alpha-trioxymethylene). 0.5 part of diethyl dioxide, and 0.2 part of sulfuric acid. The vessel is closed and charged with ethylene to a pressure of 300 atmospheres.

v The vessel is then slowly heated to between 148 and.164 C: with agitation. At this temperature the ethylene pressure is adjusted to 910 atmos-- pheres and held in the range of 920 to 980 atmospheres for 9.75 hours. During this period a total pressure drop of 60 atmospheres is observed- The range throughout the period of reaction by repressuring wlthethylene. Upon completion of the reaction the vessel is cooled and the unreacted-gases-bled 01!. From the reaction mixture there is obtained a white granular mass from which there is isolated a polymer having a composition corresponding to an ethylene/formaldehyde mole ratio 0129 to 1 and melting at 99 to 100 C. The polymer is thermosetting.

evacuated, placed in aheated shaker machine. pressured with ethylene and heating and agitationstarted; During] a reaction time of 16.5 .1

hours, throughout whichthe temperature is maintained-at to C. and the pressure at -'l60 to 955 atmospheres, there is a total observed pressure dropzof 180 atmospheres. The product-analyzes 77.2% carbon, from which it may be calcu- 55 lated that the ethylene/vinyl acetate-mole ratio At the endoi this timefthe vessel is cooled, the excess ethylene bled oil. arid the contents discharged. The crude reaction v mixture, amounting to 105v parts is steamdistilled to separate the tertiary-butyl alcohol and volatilize the major portion of the There is thus obtained 22 Y N-vinylphthalimide. parts ofa strong elastomer of ethylene. and N- vinylphthalimide mole ratio is 5.3 to The 95 to 100 'C., have a tensile strength of. 1530 lbs/sq. in. and an elongation at break of 380%. f

' Example. 8.A stainless'steel lined reaction vessel is chargedapproximately two-fifths full witha solution of 0.5mm ofdimethyl dioxide in 1 parts of distilled water. The vessel is closed,

7 placedin aheatedshaker machine, pressured with purenitrogen and is charged with'100. rts 75 with ethylene. and heating and agitation started.

- a "let-down During reaction time of 9% hours, throughout which the temperature is raisedslowly from 125 to 202 C., and the pressure maintained between 600 and 900 atmospheres by periodically repressuring with ethylene, there is a total observed pressure drop of 1025 atmospheres. At the end of this time, the vessel .is cooled, the excess ethylene bled off and the contents of the reaction vessel discharged. There are thus obtained 75 parts of a tough, flexible ethylene polymer with a tensile strength of- 1420 lbs/sq. in.

Example 9.A stainless steel lined reaction vessel is charged approximately two-fifths full with 150 parts of deaerated, distilled water and 1 part of diethyl dioxide. The vessel is closed, placed in a heated shaker machine, pressured with ethylene, and heating and agitation started. During a reaction time of 9% hours, throughout which the temperature is maintained at 118 to 130 0., and the pressure at 790 to 910 atmospheres, there is a total observed pressure drop of 945 atmospheres. The vessel is then cooled, the excess ethylene is bled off, and the contents of the vessel discharged. There are thus obtained 61 parts of a white, tough ethylene polymer with a tensile strength of 2500 lbs/sq. in.

Example 10.-Through a tubular, strainless steel reaction vessel I. D. x 34' in length are passed 1000 cc./hr. of deaerated, distilled water containing 0.2% of diethyl dioxide and 1% of borax together with ethylene at 1000 atmospheres pressure. The reaction vessel is immersed in liquid, the temperature of which is maintained at 165 to 170 C. The product is continuously discharged into an atmospheric pressure separator, from which the exit gas is continuously discharged through a meter, and from which solid and liquid are removed periodically, by means of valve between reaction vessel and separator, which valve is so adjusted as to maintain the exit gas rate at about 15 cu. ft./hr. (measured at room temperature and pressure). In six hours of such operation there are obtained 2640 parts of white, solid ethylene polymer which is a conversion of 50% of the ethylene charged to solid polymer. This polymer is tough and flexible, can be cold drawn, and has a tensile strength of 1100 lbs/sq. in. based on the original dimensions of the test sample.

Example 11.The process of Example 10 is duplicated except that the concentration of diethyl dioxide catalyst in the aqueous phase is decreased from 0.2% to 0.008%. In five hours of such operation there are obtained 579 parts of white, solid polymer, a conversion of 21% of the ethylene charged to solid polymer. This polymer has a tensile strength of 1660 lbs/sq. in.

Example 12.-The process of Example 11 is duplicated, except that benzene is also pumped through the reaction vessel with the aqueous solution of diethyl dioxide and borax and the ethylene, at a rate of approximately 250 cc./hr. In six hours of such operation there are obtained 690 parts of solid ethylene polymer, similar to that of Example 11, but with an even higher tensile strength, 2075 lbs./sq. in. Twenty per cent of the ethylene charged is converted to solid polymer in this type of operation.

Example 13.The polymerization of ethylene was conducted in a pressure-resisting tu'be having an internal diameter of an external diameter of 1 /2" and a total overall length of 88'. Ethylene was introduced into the tube at a rate of 16.2 lbs./hr., at a pressure of 1000 atmospheres, together with 3.5 lbs. of benzene. 21.5 lbs/hr. of

water, preheated to 217 C., was introduced with the ethylene and benzene at the entrance of the converter. There was introduced into the converter at a point 12' from the entrance 10.4 lbs. of water per hour containing 0.011% of diethyl peroxide; at a second point 17 from thefirst point, water containing 0.011% diethyl peroxide was introduced at the rate of 9.8 lbs./hr.; at a third point 21 from the second, water containing 0.011% diethyl peroxide was introduced at the rate of 9.6 lbs/hr. The tube was maintained at a temperature of 229 C. by external heating means. Reaction products were continuously let down to atmospheric pressure, and the polymeric ethylene recovered, whereupon a conversion of 22.5% was realized with substantially quantitative yield.

The optimum temperature for the present process varies considerably with the nature of the material polymerized. In discontinuous or batch operation, temperatures in excess of about 200 C. are generally not employed because under such conditions the diethyl dioxide decomposes too rapidly and at temperatures below 60 C. polymerization is too slow for practical purposes.

The present catalysts are effective for the polymerization of ethylene at temperatures in the range of to 275 C. or above. Under ethylene polymerization conditions, e. g., between 205 and 300 C. the catalysts are efficient, especially in those reactions conducted continuously (in contrast to batch operation) which require but a comparatively short time of contact say up to 30 minutes or less.

The catalysts of this invention show particular utility in the preparation of interpolymers of ethylene with organic compounds having at least one polymer producing unsaturated linkage, e. g., in the polymerization of ethylene with another containing a polymer producing unsaturated linkage, e. g., vinyl acetate, vinyl chloride, methacrylic acid esters, vinyl thiolacetate, etc.

The dialkyl dioxidecan be used at practically any pressure depending on the requirement of the compound being polymerized.

Although the purity of reactants is not critical to operativeness, it is preferable to use reagents as pure as is commercially feasible. In general the process is operated under conditions such that I Q the molecular oxygen content of the system, based upon the ethylene (and the unsaturated compound, if present), for example, is less than 1000 parts per million, under 200 parts per million being preferred and under 20 parts per million giving attractive products. I

The process can be operated at pressures ranging from atmospheric to 3000 atmospheres and above, depending upon the compound being polymerized, it being preferred to use superatmospheric pressures of the order of 200 atmospheres and above.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

-I claim:

1. In a continuous process for homopolymerizing ethylene at a pressure above at least 1000.

atmospheres. the steps which comprise passing ethylene together with a dialkyl dioxide of the formula. ROOR' in which R and R unsubstituted alkyl groups,

are simple containing from 1 to 3 carbon atoms into a reaction zone of relatively 3 great length to diameter, conducting the reaction therein at a temperature between 205 and 300 C. and with a contact time of not more than thirty minutes and continuously removing from the reaction zone the homopolymer produced.

2. In a continuous process for homopolymerizing ethylene at a pressure above at least 1000 atmospheres, the steps which comprise passing ethylene together with a diethyl dioxide into a reaction zone or relatively great length to diameter, conducting the reaction therein at a temperature between 205 and 300 C. and with a contact time of not more than 30 minutes and continuously removing from the reaction zone the homopolymer produced.

3. In a continuous process for the homopoiymerization of ethylene at a pressure above at 'least 1000 atmospheres, the steps which comprise passing ethylene, benzene, and diethyl dioxide into a reaction zone of relatively great length to diameter, conducting the reaction therein at a temperature between 205 and 300 C., and with a contact time of not more than 30 minutes, and continuously removing from the 25 8 reaction zone the ethylene, homopolymer produeed.

BERLIN D. PETERSON.

REFERENCES CITED lhe following references are of record in the flle of this patent:

UNITED STATES PATENT Number Number 

